Precision casting mold and method of producing the same

ABSTRACT

Provided is a precision casting mold to be used to produce a cast product. The precision casting mold includes a core having a shape corresponding to an internal hollow portion of the cast product and an outer mold corresponding to a shape of an outer peripheral surface of the cast product, and the outer mold is made up of: a prime layer which is formed on an inner peripheral surface and is formed from a slurry film obtained by drying slurry for the precision casting mold including mono-dispersed ultrafine alumina particles having a particle size of 1.0 μm or smaller; and a multi-layered backup layer which is formed on the outside of the prime layer by repeatedly forming a first backup layer obtained by forming and drying a slurry layer formed from the slurry for the precision casting mold and a stucco layer in which silicon carbide (SiC) as a stucco material is adhered to the slurry layer.

FIELD

The present invention relates to a precision casting mold and a method of producing the same.

BACKGROUND

There is a precision casting method used in the case of producing a cast product with high precision as a casting method of producing a cast product. In the precision casting method, as disclosed in Patent Literature 1, slurry is applied around a lost foam pattern (wax pattern) having the same shape as a molded component and then a first stucco (flour) layer is adhered to it and is then subjected to a drying treatment. Thereafter, three operations of the application of the slurry, the adhesion of the stucco, the drying are repeatedly performed, thereby producing a pattern for covering the outside (outer mold) of the cast product.

Here, the precision casting mold is formed in such a manner that the wax pattern is placed in slurry mainly including a silica sol, the slurry is adhered to the surface of the wax pattern, and then the slurry is dried.

Since the slurry adhered by single operation is only less and thin, the operation is repeatedly performed from several to ten times to obtain the thickness. In addition, coarse particles called a stucco material are sprinkled and adhered to the surface of the slurry to fast perform the drying, quickly ensure the thickness, or prevent dry cracks. Therefore, a dense layer and a coarse particle layer are repeated in the cross-sectional structure of the mold.

For example, the silica sol is a solution in which spherical silica particles having a particle size of about 20 nm are dispersed. When the ultrafine silica particles are adhered to the surface of relatively fine particles (from several microns to scores of microns) and coarse particles (stucco) (hundreds of microns to several millimeters) such as zircon or alumina contained in the slurry during the drying and are tightly bonded to each other by drying and heat treatment, the shape of the mold is maintained and strength is also held, so that it is possible to use as a mold.

CITATION LIST Patent Literature

Patent Literature 1: Japanese Patent Application Laid-open No. 2001-18033

SUMMARY Technical Problem

In the precision casting mold, however, thickness and strength are ensured by repeatedly performing slurry adhesion operation, stucco adhesion operation, and drying operation on the surface of a wax pattern.

Particularly, in the stucco adhesion operation, in order to fast perform the drying, to quickly ensure a thickness, and to prevent dry cracks, a silica-based particle material or an alumina-based particle material are used as the stucco.

Since the mold is produced by laminating several layers (ten layers) including a slurry layer and a stucco layer and the cross-sectional structure of the mold has a dense layer and a coarse particle layer which are repeatedly laminated, there are problems that thermal conductivity is low and temperature control is difficult during unidirectional solidification.

Accordingly, a mold has been required in which thermal conductivity is high and a temperature gradient is easily controlled during solidification, so that the improvement of cast product yield and the improvement of strength properties can be expected.

The present invention has been achieved in consideration of the above problem and an object thereof is to provide a precision casting mold in which thermal conductivity is high and a method of producing the same.

Solution to Problem

According to a first aspect of the present invention in order to solve the above mentioned problems, there is provided a precision casting mold which is used to produce a cast product, including: a core having a shape corresponding to an internal hollow portion of the cast product; and an outer mold corresponding to a shape of an outer peripheral surface of the cast product, wherein the outer mold is made up of: a prime layer which is formed on an inner peripheral surface and is formed from a slurry film obtained by drying slurry for the precision casting mold; and a multi-layered backup layer which is formed on the outside of the prime layer by repeatedly forming a backup layer obtained by forming and drying a slurry layer formed from the slurry for the precision casting mold and a stucco layer in which silicon carbide as a stucco material is adhered to the slurry layer.

According to a second aspect of the present invention, there is provided the precision casting mold according to the first aspect, wherein the prime layer has the stucco layer in which the stucco material is adhered to the slurry layer formed from the slurry for the precision casting mold.

According to a third aspect of the present invention, there is provided a method of producing a precision casting mold which is used to produce a cast product, the method including: a first film forming process in which a precision casting wax pattern is immersed and pulled up into/from slurry for the precision casting mold and then a drying treatment is performed, thereby forming a prime layer, which is formed from a slurry film, on a surface of the wax pattern; a second film forming process in which silicon carbide used as a stucco material is sprinkled on a surface of the slurry after the wax pattern formed with the prime layer is immersed and pulled up into/from the slurry for the precision casting mold and then a drying treatment is performed, thereby forming a backup layer; a molded body forming process in which the second film forming process of forming the backup layer is repeated more than once, thereby obtaining a molded body formed with a multi-layered backup layer; a wax removing process in which wax of the wax pattern is melted and removed from the obtained molded body; and a mold firing process in which the molded body obtained after the wax removal is subjected to a firing treatment, thereby obtaining a mold.

According to a fourth aspect of the present invention, there is provided the method of producing the precision casting mold according to the third aspect, wherein silicon carbide used as a stucco material is adhered to a slurry layer formed from the slurry for the precision casting mold to form a stucco layer and the stucco layer is dried during the first film forming process.

Advantageous Effects of Invention

According to the present invention, silicon carbide is used as a stucco material, and thus it is possible to advantageously obtain a mold in which thermal conductivity is high and a temperature is easily controlled during unidirectional solidification.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a configuration diagram of a dried molded body which is an outer mold.

FIG. 2 is a configuration diagram of another dried molded body which is an outer mold.

FIG. 3 is a flowchart illustrating an example of processes in a casting method.

FIG. 4 is a flowchart illustrating an example of processes in a method of producing a mold.

FIG. 5 is an explanatory diagram schematically illustrating a process of producing a core.

FIG. 6 is a perspective view schematically illustrating a part of a metal mold.

FIG. 7 is an explanatory diagram schematically illustrating a process of producing a wax pattern.

FIG. 8 is an explanatory diagram schematically illustrating a configuration in which slurry is applied on the wax pattern.

FIG. 9 is an explanatory diagram schematically illustrating a process of producing the outer mold.

FIG. 10 is an explanatory diagram schematically illustrating some processes in the method of producing the mold.

FIG. 11 is an explanatory diagram schematically illustrating some processes in a casting method.

DESCRIPTION OF EMBODIMENTS

Hereinafter, the present invention will be described in detail with reference to the drawings. Furthermore, the present invention is not limited to the following description. Further, components in the following description include those which are easily conceived by persons skilled in the art, those which are substantially identical thereto, and those in a scope of so-called equivalents.

FIG. 1 is a configuration diagram of a dried molded body of an outer mold. FIG. 2 is a configuration diagram of another dried molded body of an outer mold.

As illustrated in FIG. 1, a precision casting mold is a precision casting mold to be used to produce a cast product and includes a core having a shape corresponding to an internal hollow portion of the cast product and an outer mold corresponding to a shape of an outer peripheral surface of the cast product, and the outer mold is made up of: a prime layer (first dried film) 101A which is formed on an inner peripheral surface and is formed from a slurry film obtained by drying slurry for the precision casting mold including mono-dispersed ultrafine alumina particles having a particle size of 1.0 μm or smaller; and a multi-layered backup layer 105A which is formed on the outside of the prime layer (first dried film) 101A by repeatedly forming a first backup layer (second dried film) 104-1 obtained by forming and drying a slurry layer 102 formed from the slurry for the precision casting mold and a stucco layer 103 in which silicon carbide (SiC) as a stucco material is adhered to the slurry layer 102.

Here, the fine alumina particles (ultrafine alumina particles) of high purity ultrafine particles, which are subjected to mono-dispersion using, for example, a ball mill as a dispersion means, are used as a binder forming the slurry in the present invention.

The term “mono-dispersion” used herein refers to a state of being mono-dispersed into 0.5 μm even in a result of a dispersion treatment when the slurry is formed using, for example, ultrafine alumina particles having a particle size of about 0.5 μm.

Here, the particle size of the ultrafine alumina particles is 1.0 μm or smaller and more preferably may be in the range of 0.3 to 0.6 μm.

In the present invention, the reason why the fine alumina particles are preferably 1.0 μm or smaller in size is because results of a bending strength test are undesirable when the fine alumina particles exceed 1.0 μm in size.

Zircon powders (for example, having a size of 350-mesh) as flour are added to the binder of the mono-dispersed ultrafine alumina particles, thereby obtaining the slurry for the precision casting mold.

Further, in the present invention, a case where the flour is not added may be also acceptable.

Here, polycarboxylic acid salts (for example, ammonium salts) are used to be mono-dispersed as a dispersing agent.

In addition, a ball mill using, for example, balls having a diameter of 10 to 20 mm can be exemplified as the dispersion means, but the dispersion means is not limited thereto as long as being a means that mono-disperses.

In the present invention, it is important to obtain good slurry by mono-dispersing the ultrafine alumina particles serving as the binder.

Furthermore, in the present invention, the silicon carbide (SiC) is used as the stucco material.

The silicon carbide having an average particle size of about 0.8 mm is used. Further, an allowable average particle size is preferably about 0.46 to 1.2 mm.

In the present invention, since the silicon carbide (SiC) particles having the high thermal conductivity are used as the stucco material, the mold is obtained in which the thermal conductivity is high and the temperature is easily controlled during the unidirectional solidification.

Next, a method of producing the precision casting mold will be described with reference to FIGS. 1 and 2.

(First Film Forming Process)

First, in the first film forming process, a wax pattern 30 is immersed and then pulled up into/from the slurry for the precision casting mold including the mono-dispersed ultrafine alumina particles having a particle size of 1.0 μm or smaller (hereinafter, referred to as “slurry”), and excess slurry is dropped. Thereafter, a slurry film (first dried film) is obtained on the surface of the wax pattern 30 by a drying treatment.

In FIG. 1, the slurry film is the prime layer 101A which comes in contact with the surface of the wax pattern 30.

(Second Film Forming Process)

Next, the wax pattern 30 having the prime layer 101A is immersed and is then pulled up into/from the slurry, and the excess slurry is dropped, thereby forming the slurry layer (second layer) 102. Silicon carbide particles (having an average particle size of 0.8 mm) as the stucco material are sprinkled (stuccoed) on the wet slurry layer (second layer) 102 as a stucco material, thereby forming the stucco layer (first layer) 103 adhered with the stucco material. A laminated structure of the slurry layer (second layer) 102 and the stucco layer (first layer) 103 is dried, so that the first backup layer (second dried film) 104-1 is formed on the prime layer (first dried film) 101A.

(Molded Body Forming Process)

The similar operation as the second film forming process of forming the first backup layer 104-1 is repeated more than once (for example, 6 to 10 times), thereby obtaining a dried molded body 106A which is the outer mold having a predetermined thickness of the multi-layered backup layer 105A in which the slurry layer ((n+1)-th layer) 102 and the stucco layer (n-th layer) 103 are alternately laminated.

The dried molded body is put in, for example, an autoclave of 150° C., so that wax constituting the wax pattern 30 is melted and then is discharged.

Thereafter, the pattern is subjected to a heat treatment at 1,000° C., thereby obtaining the precision casting mold.

Since the precision casting mold is obtained using the silicon carbide particles as the stucco material having the high thermal conductivity, it is possible to obtain the mold in which the thermal conductivity is high and the temperature is easily controlled during the unidirectional solidification. In contrast, since the silica-based particles or the alumina-based particles are used as the stucco material in the related art, the thermal conductivity is low and the temperature is difficult to be controlled during the unidirectional solidification.

Here, the comparison of the thermal conductivity of the silicon carbide with the thermal conductivity of the conventional alumina, zirconia, silica, or molten silica is indicated in Table 1.

TABLE 1 Stucco material Thermal conductivity (W/m · k) Silicon carbide (SiC) 200 Alumina (Al₂O₃) 30 Zirconia (YSZ) 2 Silica (SiO₂) 10 Molten silica 2

As indicated in Table 1, in the present invention, since the silicon carbide having the thermal conductivity is used as the stucco material, it is possible to obtain the mold in which the thermal conductivity is high and the temperature is easily controlled during the unidirectional solidification.

In addition, as illustrated in FIG. 2, a prime stucco layer 101 b adhered with the silicon carbide (SiC) as the stucco material may be formed on a prime slurry layer 101 a in a prime layer 101B and may be then dried, thereby forming the prime layer 101B.

Further, as in the prime layer 101B, when the stucco material is adhered, it is possible to obtain a dried molded body 106B of an outer mold having the multi-layered backup layer 105B in which the slurry layer 102 and the stucco layer 103 of the multi-layered backup layer 105B have the same laminated number (n layers).

In the present invention, although zircon powders were used as flour, it is possible to obtain the similar precision casting mold even when alumina powders other than the zircon powders are used as the flour and alumina stucco particles are used instead of the zircon stucco particles as a stucco material.

Further, the relation between the flour and the stucco material is not limited, but either of the zircon powders or the alumina powders may be used as the flour and either of the zircon stucco particles or the alumina stucco particles may be used as the stucco material.

Although the particle size of the flour is 350-mesh, the present invention is not limited thereto, but preferably uses particles of, for example, about 5 to 80 μm and particles having an average particle size of, for example, 50 μm or smaller.

Although the particle size of the stucco particles is 0.8 mm, the present invention is not limited thereto, but preferably uses particles of, for example, about 0.4 mm to 2 mm and particles having an average particle size of, for example, 0.5 mm or larger.

A casting method using the precision casting mold according to the present invention will be described below.

FIG. 3 is a flowchart illustrating an example of processes in the casting method. The casting method will be described below with reference to FIG. 3. Here, the processes illustrated in FIG. 3, may be fully automatically executed and may be executed in such a manner that an operator operates each of apparatuses for executing each of the processes. In the casting method of the present embodiment, a mold is produced (step S1). The mold may be previously produced and may be produced every time a casting process is executed.

The method of producing the mold to be executed in step S1 will be described below with reference to FIGS. 4 to 10. FIG. 4 is a flowchart illustrating an example of processes in the method of producing the mold. Here, processes illustrated in FIG. 4, may be fully automatically executed and may be executed in such a manner that an operator operates each of apparatuses for executing each of the processes.

In the method of producing the mold, a core is produced (step S12). The core has a shape corresponding to an internal hollow of a cast product to be produced with the mold. That is, the core is disposed at a portion corresponding to the internal hollow of the cast product and prevents inflow of a metal, which is a material for the cast product, during casting. Hereinafter, a process of producing the core will be described with reference to FIG. 5. FIG. 5 is an explanatory diagram schematically illustrating the process of producing the core. In the method of producing the mold, as illustrated in FIG. 5, a metal mold 12 is prepared (step S101). The metal mold 12 has a hollow region corresponding to the core. The hollow portion of the core is a convex portion 12 a. Further, in FIG. 5, the metal mold 12 is illustrated in cross section, but the metal mold 12 becomes basically the hollow for covering an entire periphery of the region corresponding to the core, except for an opening through which a material is poured into a space and a hole through which air is discharged. In the method of casting the mold, as indicated by an allow 14, ceramic slurry 16 is poured into the inside of the metal mold 12 from the opening through the material is poured into the space of the metal mold 12. Specifically, a core 18 is produced by so-called injection molding which sprays the ceramic slurry 16 into the inside of the metal mold 12. In the method of producing the mold, after the core 18 is produced inside the metal mold 12, the core 18 is detached from the metal mold 12 and the detached core 18 is placed in a firing furnace 20, thereby being fired. Thus, the core 18 formed of a ceramic is fired and hardened (step S102). In the method of casting the mold, the core 18 is produced in the manner described above. Further, the core 18 is formed of a material capable of being removed with a core removing treatment such as a chemical treatment after the cast product is hardened.

In the method of producing the mold, after the core 18 is produced, an external metal mold is produced (step S14). The external metal mold has a shape in which an inner peripheral surface thereof corresponds to the outer peripheral surface of the cast product. The metal mold may be formed of a metal or may be formed of a ceramic. FIG. 6 is a perspective view schematically illustrating a part of the metal mold. A metal mold 22 a illustrated in FIG. 6 is configured such that a concave portion formed on the inner peripheral surface corresponds to the outer peripheral surface of the cast product. Further, in FIG. 6, only the metal mold 22 a is illustrated, but corresponding to the metal mold 22 a, a metal mold corresponding to the metal mold 22 a is also produced in a direction to close the concave portion formed on the inner peripheral surface. The method of producing the mold is a type in which the inner peripheral surface corresponds to the outer peripheral surface of the cast product when two metal molds are fitted to each other.

In the method of producing the mold, after the external metal mold is produced, a wax pattern is produced (step S16). The description will be made below with reference to FIG. 7. FIG. 7 is an explanatory diagram schematically illustrating a process of producing the wax pattern. In the method of producing the mold, the core 18 is installed at a predetermined position of the metal mold 22 a (step S110). Thereafter, a metal mold 22 b corresponding to the metal mold 22 a covers a surface on which the concave portion of the metal mold 22 a is formed, so that the metal molds 22 a and 22 b surround the periphery of the core 18 and a space 24 is formed between the core 18 and the metal molds 22 a and 22 b. In the method of producing the mold, as indicated by an arrow 26, a pouring of a WAX 28 starts to be poured from a pipe connected to the space 24 into the inside of the space 24 (step S112). The WAX 28 is, for example, wax of a relatively low-melting point material which is melted when being heated to a predetermined temperature or higher. In the method of producing the mold, the entire region of the space 24 is filled with the WAX 28 (step S113). Thereafter, the WAX 28 encloses around the core 18 by solidifying the WAX 28, thereby forming the wax pattern 30. The wax pattern 30 is a wax pattern in which a portion formed of the WAX 28 has basically the same shape as the cast product of the production object. Thereafter, in the method of producing the cast product, the wax pattern 30 is separated from the metal molds 22 a and 22 b and then a sprue 32 is attached to the wax pattern (step S114). The sprue 32 is a mouth into which a molten metal, which is a metal melted during casting, is introduced. In the method of producing the mold, the wax pattern 30 formed of the WAX 28 is produced in the manner described above so as to have the same shape as the cast product and include the core 18 therein.

In the method of producing the mold, after the wax pattern 30 is produced, slurry is applied (dipped) (step S18). FIG. 8 is an explanatory diagram schematically illustrating a configuration in which the slurry is applied on the wax pattern. In the method of producing the mold, as illustrated in FIG. 8, the wax pattern 30 is immersed into a storage portion 41, in which slurry 40 is stored, and then is dried after being taken out therefrom (step S19). Thus, the prime layer 101A can be formed on the surface of the wax pattern 30.

Here, the applied slurry in step S18 is slurry which is directly applied on the wax pattern 30. The ultrafine alumina particles are used for the slurry 40. In the slurry 40, for example, zirconia having refractory fine particles of about 350-mesh is preferably used as flour. In addition, polycarboxylic acid salts are preferably used as a dispersing agent. In addition, a trace of an antifoaming agent (silicon-based substance) or a wettability improving agent of, for example, 0.01% is preferably added to the slurry 40. By the addition of the wettability improving agent, adhesive property of the slurry 40 can be improved with respect to the wax pattern 30.

In the method of producing the mold, as illustrated in FIG. 8, a slurry application is performed with the slurry 40, and the applied slurry is dried, so that the wax pattern having the prime layer (first dried film) 101A is further applied (dipped) with the slurry (step S20). As illustrated in FIG. 9, stuccoing process of sprinkling the silicon carbide particles (having an average particle size of 0.8 mm) as a stucco material 54 is performed on the surface of the wet slurry (step S21). Thereafter, the stucco material adhered to the surface of the slurry layer is dried, thereby forming the first backup layer (second dried film) 104-1 on the prime layer (first dried film) 101A (step S22).

A process of determining whether the similar operation as the forming process of the first backup layer (second dried film) 104-1 is repeated more than once (for example, n: six to ten times) is performed (step S23). An n-th backup layer 104-n is laminated by a predetermined number of times (n) (step S23: Yes), thereby obtaining the dried molded body 106A which is the outer mold formed with the multi-layered backup layer 105A having the thickness of, for example, 10 mm.

In the method of producing the mold, after the dried molded body 106A having the multilayer structure is obtained which is formed with the prime layer 101A and the multi-layered backup layer 105A, the dried molded body 106A is subjected to a heat treatment (step S24). Specifically, the WAX between the outer mold and the core is removed, and the outer mold and the core are further fired. The description will be made below with reference to FIG. 10. FIG. 10 is an explanatory diagram schematically illustrating some processes of the method of producing the mold. In the method of producing the mold, as illustrated in step S130, the dried molded body 106A which is the outer mold having the multilayer structure formed with the prime layer 101A and the multi-layered backup layer 105A is put in an autoclave 60 and then is heated. The inside of the autoclave 60 is filled with pressurized steam, and thus the wax pattern 30 inside the dried molded body 106A is heated by the pressurized steam. Thus, the WAX constituting the wax pattern 30 is melted and the melted WAX 62 is discharged from a space 64 surrounded by the dried molded body 106A.

In the method of producing the mold, when the melted WAX 62 is discharged from the space 64, as illustrated in step S131, a mold 72 is produced in which the space 64 is formed in a region filled with the WAX between the dried molded body 106A which is the outer mold and the core 18. Thereafter, in the method of producing the mold, as illustrated in step S132, the mold 72 having the space 64 formed between dried molded body 106A which is the outer mold and the core 18 is heated by a firing furnace 70. Thus, in the mold 72, a water component or an unnecessary component contained in the dried molded body 106A which is the outer mold is removed and an outer mold 61 is formed by being further fired and cured. In the method of producing the cast product, the mold 72 is produced in the manner described above.

The casting method will be continuously described with reference to FIGS. 3 and 11. FIG. 11 is an explanatory diagram schematically illustrating some processes of the casting method. In the casting method, after the mold is produced in step S1, the mold is pre-heated (step S2). For example, the mold is disposed in a furnace (vacuum furnace, firing furnace) and is heated to 800° C. or higher and 900° C. or lower. By the pre-heating, it is possible to suppress the damage of the mold when the molten metal (melted metal) is poured into the mold at the time of producing the cast product.

In the casting method, after the mold is pre-heated, the molten metal is poured (step S3). That is, as illustrated in step S140 of FIG. 11, a molten metal 80, that is, a dissolved raw material (for example, steel) of the cast product is poured between the outer mold 61 and the core 18 from the opening of the mold 72.

In the casting method, after the molten metal 80 poured into the mold 72 is solidified, the outer mold 61 is removed (step S4). That is, as illustrated in step S141 of FIG. 11, after the molten metal 80 is hardened inside the mold 72 and becomes a cast product 90, the outer mold 61 is crushed and is then removed from the cast product 90 as a fragment 61 a.

In the casting method, after the outer mold 61 is removed from the cast product 90, a core removing treatment is performed (step S5). That is, as illustrated in step S142 of FIG. 11, the cast product 90 is put in an autoclave 92 and is subjected to the core removing treatment, so that the core 18 inside the cast product 90 is dissolved and a dissolved core 94 is discharged from the inside of the cast product 90. Specifically, the cast product 90 charged into an alkaline solution inside the autoclave 92 is repeatedly pressurized and depressurized, so that the dissolved core 94 is discharged from the cast product 90.

In the casting method, after the core removing treatment is performed, a finishing treatment is performed (step S6). That is, the finishing treatment is performed on the surface or the interior of the cast product 90. Furthermore, in the casting method, inspection of the cast product is performed along with the finishing treatment. Thus, as illustrated in step S143 of FIG. 11, a cast product 100 can be produced.

In the casting method of the present embodiment, as described above, the mold is produced by a lost-wax casting method using WAX (wax), thereby producing the cast product. Here, in the method of producing the mold, the casting method, and the mold of the present embodiment, the outer mold having the multilayer structure which is the outside of the mold is formed in such a manner that the prime layer (first dried film as a first layer) 101A serving as the inner peripheral surface is formed using the ultrafine alumina particles as the slurry and the multi-layered backup layer 105A including the slurry layer and the stucco layer formed using the silicon carbide particles is formed on the outside of the prime layer 101A.

In addition, as described above, the prime layer may be the prime layer 101B including the slurry layer 101 a added with the silicon carbide as a stucco material and the stucco layer 101 b.

Example 1

The method of producing the mold and the casting method of the present embodiment will be described below using Examples. Further, in the following Examples, a front wax pattern formed with an outer mold was a member having a width of 30 mm, a thickness of 8 mm, and a length of 300 mm, and a prime layer (first dried film) formed from a slurry layer and a multi-layered backup layer made of slurry and a stucco material are formed in the wax pattern, thereby producing a mold.

High-purity ultrafine alumina particles (Al₂O₃, having a specific surface area of 10 m²/g and a particle size of about 0.5 μm) were kneaded with a ball mill for 24 hours using polycarboxylate ammonium as a dispersing agent and thus were formed in a slurry form. A solid content concentration of the obtained slurry is 50 wt %.

It was confirmed that the resulting alumina particles of a dispersion treatment was mono-dispersed into 0.5 μm in the slurry.

Zircon powders of 350-mesh were added to the slurry as flour, thereby forming slurry for a precision casting mold.

Further, at the same time, a silicon-based substance as an antifoaming agent of 0.01% and a wettability improving agent of 0.01% were added to make as in-use slurry.

A wax body having a width of 30 mm, a thickness of 8 mm, and a length of 300 mm was prepared, after the wax body was immersed and then pulled up into/from the obtained in-use slurry, thereby adhering the in-use slurry to the surface of the wax, excess in-use slurry was dropped and a prime layer (first dried film) of the slurry was obtained on the surface of the wax body by a drying treatment.

Next, in order to obtain a second dried film, the wax body having the prime layer was immersed and then pulled up into/from the in-use slurry and excess slurry was dropped.

Silicon carbide particles having an average particle size of 0.8 mm were adhered to wet in-use slurry and then were dried, so that a second dried film (first backup layer) was formed.

The similar operation as the second dried film (first backup layer) forming process was repeated six times, so that a molded body having a multi-layered backup layer was obtained to have a thickness of about 10 mm. The obtained dried molded body was put in an autoclave of 150° C., so that the wax was melted and then was discharged.

Thereafter, the wax pattern was subjected to a heat treatment at 1000° C., thereby obtaining the mold of Example 1.

Example 2

Slurry obtained by adding alumina powders of 350-mesh as flour instead of the zircon powders in Example 1 was used for slurry for a precision casting mold.

In addition, a mold of Example 2 was obtained by the similar operation as in Example 1 except for using alumina stucco particles having an average particle size of 0.8 mm as a stucco material.

Since the silicon carbide (SiC) particles having the high thermal conductivity were used as the stucco material, the mold was obtained in which the thermal conductivity was high and in which the temperature was easily controlled during the unidirectional solidification.

Since the temperature gradient can be increased during solidification by the improvement of the thermal conductivity of the mold, it is possible to improve the cast product yield and to improve the strength properties.

REFERENCE SIGNS LIST

-   -   12, 22 a, 22 b METAL MOLD     -   12 a CONVEX PORTION     -   14, 26 ARROW     -   16 CERAMIC SLURRY     -   18 CORE     -   20, 70 FIRING FURNACE     -   24, 64 SPACE     -   28 WAX     -   30 WAX PATTERN     -   32 SPRUE     -   40 SLURRY     -   60, 92 AUTOCLAVE     -   61 OUTER MOLD     -   61 a FRAGMENT     -   62 DISSOLVED WAX     -   72 MOLD     -   80 MOLTEN METAL     -   90, 100 CAST PRODUCT     -   94 DISSOLVED CORE     -   101A, 101B PRIME LAYER     -   102 SLURRY LAYER     -   103 STUCCO LAYER     -   104-1 FIRST BACKUP LAYER     -   104-n n-TH BACKUP LAYER     -   105A, 105B MULTI-LAYERED BACKUP LAYER 

1. A precision casting mold which is used to produce a cast product, comprising: a core having a shape corresponding to an internal hollow portion of the cast product; and an outer mold corresponding to a shape of an outer peripheral surface of the cast product, wherein the outer mold is made up of: a prime layer which is formed on an inner peripheral surface and is formed from a slurry film obtained by drying slurry for the precision casting mold including ultrafine alumina particles having a particle size of 0.3 μm to 0.6 μm; and a multi-layered backup layer which is formed on the outside of the prime layer by repeatedly forming a backup layer obtained by forming and drying a slurry layer formed from the slurry for the precision casting mold and a stucco layer in which silicon carbide as a stucco material is adhered to the slurry layer.
 2. The precision casting mold according to claim 1, wherein the prime layer has the stucco layer in which the stucco material is adhered to the slurry layer formed from the slurry for the precision casting mold.
 3. A method of producing a precision casting mold which is used to produce a cast product, the method comprising: a first film forming process in which a precision casting wax pattern is immersed and pulled up into/from slurry for the precision casting mold including ultrafine alumina particles having a particle size of 0.3 μm to 0.6 μm and then a drying treatment is performed, thereby forming a prime layer, which is formed from a slurry film, on a surface of the wax pattern; a second film forming process in which silicon carbide used as a stucco material is sprinkled on a surface of the slurry after the wax pattern formed with the prime layer is immersed and pulled up into/from the slurry for the precision casting mold and then a drying treatment is performed, thereby forming a backup layer; a molded body forming process in which the second film forming process of forming the backup layer is repeated more than once, thereby obtaining a molded body formed with a multi-layered backup layer; a wax removing process in which wax of the wax pattern is melted and removed from the obtained molded body; and a mold firing process in which the molded body obtained after the wax removal is subjected to a firing treatment, thereby obtaining a mold.
 4. The method of producing the precision casting mold according to claim 3, wherein silicon carbide used as a stucco material is adhered to a slurry layer formed from the slurry for the precision casting mold to form a stucco layer and the stucco layer is dried during the first film forming process.
 5. The precision casting mold according to claim 1, wherein silicon carbide (SiC) used as the stucco material has an average particle size of 0.46 mm to 1.2 mm.
 6. The method of producing the precision casting mold according to claim 3, wherein silicon carbide (SiC) used as the stucco material has an average particle size of 0.46 mm to 1.2 mm. 